The technology of Carrier Aggregation (CA) has been introduced into a Long Term Evolution-Advanced (LTE-A) system in view of required improved peak rates, compatibility with a Long Term Evolution (LTE) system and full use of frequency resources. The technology of carrier aggregation refers to that there are a plurality of Component Carriers (CCs) respectively in the uplink and the downlink in a cell, and a component carrier is also referred to as a separate cell and the CC(s) serving a UE is also referred to a serving cell. In the LTE Release 8 (R8), a sub-frame includes only one Transport Block (TB) including a Media Access Control Packet Data Unit (MAC PDU). With the introduction of CA, a plurality of transport blocks can be transmitted in a sub-frame, and a transport block can be transmitted over each CC with each transport block including an MAC PDU. Both the LTE and LTE-A systems are schedule-based systems, and a base station allocates an uplink resource under a number of criteria including the amount of data in a buffer of a user equipment to be transmitted in the uplink. In order to know this information, the base station requires the user equipment to transmit a Buffer Status Report (BSR) to the base station.
Two timers including a retransmission BSR timer (retxBSR-Timer) and a BSR periodic report timer (periodicBSR-Timer) are adopted in the BSR mechanism of R8. For the retxBSR-Timer, the retxBSR-Timer is started when a BSR is reported for the first time and restarted each time the user equipment obtains a new data transmission resource but not restarted upon retransmission of data. For the periodicBSR-Timer, the periodicBSR-Timer is started when a BSR is reported for the first time and restarted when a long BSR or a short BSR is reported but not restarted when a truncated BSR is reported, where the long BSR includes 3-byte buffer information of 4 sets of logic channels, and the short BSR and the truncated BSR include 1-byte buffer information of only one set of logic channels.
A solution to control a BSR timer in a system with carrier aggregation has been absent in the prior art. The inventors have identified during a study that confliction may arise if BSR timers are controlled as in the R8 in the system with carrier aggregation so that a BSR timer is maintained respectively for each carrier. For example, at time T1, new transmission scheduling is received over a CC1 and a retxBSR-Timer of the CC1 is restarted; and retransmission data is transmitted over a CC2, and a retxBSR-Timer of the CC2 is not restarted. At time T2, the retxBSR-Timer of the CC2 expires while the retxBSR-Timer of the CC1 does not expire, and at this time, it can not be decided whether to trigger a BSR report. In another example, at time T1, an MAC PDU of the CC1 is sufficient to accommodate a long BSR, and at this time a periodicBSR-Timer is restarted; and an MAC PDU of the CC2 is only sufficient to accommodate a truncated BSR, and no periodicBSR-Timer is restarted. At time T2, the periodicBSR-Timer of the CC2 expires while the periodicBSR-Timer of the CC1 does not expire, and at this time, it can not be decided whether to trigger a BSR report either.